Explanation: In English grammar, prepositions are used to indicate the relationship between a noun or pronoun and other parts of the sentence. When it comes to time expressions, the choice of preposition depends on the specificity of the time being referred to.
1. **"At" for Specific Times**: The preposition "at" is used to indicate a specific point in time. This includes hours, minutes, and seconds. For example, "at 3:00 pm," "at 10:15 am," or "at 12:00 midnight." In the given sentence, "The train leaves Delhi at 3:00 pm and reaches Chandigarh at 7:00 pm," the preposition "at" is used correctly because it specifies the exact departure and arrival times.
2. **"On" for Dates**: The preposition "on" is used to indicate a specific date. This includes days of the week, dates, and holidays. For example, "on Monday," "on 15th July," or "on Christmas Day." Using "on" for specific times like "on 3:00 pm" is incorrect because "on" is not used for hours and minutes.
3. **"In" for Larger Time Periods**: The preposition "in" is used to indicate larger time periods such as months, years, seasons, and centuries. For example, "in July," "in 2023," "in summer," or "in the 21st century." Using "in" for specific times like "in 3:00 pm" is incorrect because "in" is not used for hours and minutes.
In the context of the given sentence, the correct preposition to use is "at" because it specifies the exact departure and arrival times of the train. The sentence "The train leaves Delhi at 3:00 pm and reaches Chandigarh at 7:00 pm" is grammatically correct and uses the appropriate preposition for the given time expressions.
Understanding the correct usage of prepositions in time expressions is crucial for clear and accurate communication, especially in contexts such as train schedules, appointments, and other time-sensitive information. This knowledge is particularly important for competitive examinations where language proficiency is tested, such as UPSC, SSC, Bank PO, CLAT, and MAT.